The source of the Geul is located at approx. 300 m (984 ft) altitude in north eastern Belgium near the German border, south of the German town of Aachen. From there, after flowing some 20 km (12 mi) in northwestern direction, it leaves Belgium and enters into the Netherlands at Cotessen in the Vaals municipality. After a further 38 km (24 mi) in west-north-western direction through the most southern part of Limburg, which in its turn is the most southern province of the Netherlands, it flows into the river Meuse, north of the city of Maastricht.
A tributary of the river Geul is the Gulp River.
Pollution problems 
The last ones of these mines have closed early in the 20th century. One of the reasons for giving up mining activities in Plombières was the occasional flooding of the mine by the river Geul, as the bedrock (mainly Carboniferous limestone) contains many faults and fissures.
Although mine factory buildings have been demolished, old railway dikes still are abundantly present in the area. They provide ideal hiking routes, that are known for the presence of so-called "zinc flora" (zinc-tolerant plants, such as yellow calamine violet and Viola calaminaria).
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